1. Field of the Invention
The present invention relates to an electric motor having a circuit apparatus therein.
2. Description of Related Art
An electric power steering (EPS) system, which assists a steering operation of a driver for steering a vehicle, is known. In an electric motor used in the EPS system, it is important to sense a rotational angle of a rotor.
Japanese Unexamined Utility Model Publication No. H05-55768U teaches a rotation sensing device, in which a permanent magnet is placed at an end part of a shaft, and a sensor is installed to a circuit board in such a manner that the sensor is opposed to the permanent magnet. In this rotation sensing device, a yoke, which has a relatively large diameter, is installed to the end part of the rotatable shaft, and the permanent magnet (pole magnet) is attached to the yoke. The sensor (pole sensor) is installed to the circuit board to oppose the permanent magnet.
However, in the case of the rotation sensing device disclosed in Japanese Unexamined Utility Model Publication No. H05-55768U, there is a possible disadvantage in terms of an assembling process thereof. For example, at the time of assembling the rotation sensing device, the yoke needs to be installed to the rotatable shaft with screws after insertion of the rotatable shaft. Furthermore, at the time of disassembling the rotor, which is integrated with the rotatable shaft, in the case of performing, for example, a maintenance work, the yoke, which is secured to the end part of the rotatable shaft with the screws, needs to be first removed from the rotatable shaft. Therefore, the time required for the assembling work or the maintenance work is disadvantageously lengthened.
Here, although the motor used in the EPS system is discussed above, the above discussed disadvantages are also found in other ordinary motors.